Modem is probably safe assumption on the end of the RJ11 lead into the top of the MK2 faceplate
Picture 2 - what is the white cable running under the Openreach socket.
Picture 3 - is that the same single cable as from the Openreach socket? Looks like maybe two cables.
Picture 4 - looks like two cables heading into a junction box
Picture 5 - a lot hinges on what is happening inside this Virgin box
Does the wire then head to picture 6
To me it looks like house was rewired for Virgin, and maybe then rewired again for BT. When the openreach faceplate is removed do any of sockets work for a telephone?
Looks very like the master socket is a fair way from where the openreach entry point is to the property, and one split pair in that wiring could impact on your actual speed.